It's not a case of once bitten twice shy for Hastings man Greg Sims, who says he's not afraid to re-enter the water after a suspected shark attack at Haumoana on Tuesday.

The 49-year-old was enjoying a dip just south of the Tukituki River mouth with partner Pauline Hayes before he was attacked at 5.30pm.

``I felt a sharp, painful bite on the back of my leg and couldn't leave the surf fast enough,' he said.

``I screamed at Pauline to get out of the water, she just stood there not comprehending what had happened.'

Mr Sims, a registered nurse, then used his towel as a tourniquet to stop the bleeding before the two drove to Hawke's Bay Hospital.

``It was the most panicked I've ever seen him,' Ms Hayes said.

The family were today still baffled over what had inflicted the bite from the blue.

``I saw nothing at all. Nothing broke the water so there was no warning and no sighting. We thought maybe it was a stingray, but from what we know they leave a sharp whip-like laceration, but this wound is the shape of a bite, and has taken a chunk of flesh away so we think it was a shark.'

Hawke's Bay Today sent a photograph of the injury to Department of Conservation scientist and shark expert Clinton Duffy, who agreed with the couple's theory.

``There appears to be a semi-circular jaw impression which indicates a shark bite,' Mr Duffy said.

``Plus it's on the upper thigh and you'd expect a typical stingray attack to be on the lower leg.

``Top of the list of suspects would be a broadnose sevengill shark (Notorhynchus cepedianus). This is a common large coastal shark species, which is most abundant near shore at this time of year.' He said the fact Mr Sims hadn't seen the shark was not surprising. ``This shark has an almost non-existent dorsal fin so you wouldn't see it break the surface in shallow water.'

The attack hadn't put Mr Sims off his favourite swimming spot.

``It'd be silly to say never again. I've been swimming here for 40 years and I've never heard of - let alone experienced - a shark attack in the area.